Hardening surface treatments for small shaft 1

[fastline12]

We have a small shaft that is approx .375diam x 3.5"L. It has an oil seal that rides on it and for that reason, it must have a very hard surface for wear resistance. It is a repair part for an OEM part. The OEM part tests approx HRC65 but with scratch methods, we believe it to be a bit harder but does not test well with the hardness tester.

Anyway, we previously specified machining of 8620 and carburizing, then grinding the OD to dimension.

We have lost of vendor for this work and cannot find anyone within our budget for them. For this reason, we are looking to determine if there are any other processes that can be considered to create a hard treatment? The structure of the part is not much concern. really any alloy steel will do as long as we achieve our surface hardness goals.

We also have a 1/4" thread at one and one of the things that is running cost up is having to machine, treat, grind, hard turn threads. We need to cut a step in there somewhere. A treatment that can be applied to a threaded shaft would be great but I should probably run some numbers before saying that due to brittle threads.

If there is a hardening treatment we could do in shop, that would be great but that might be reaching.

 

[handleman]

Can you purchase induction-hardened, pre-ground linear shaft material (like a Thomson shaft) and then cut the threads? It will come in smooth as glass and over HRC60 to a 1~2mm depth. You can then turn off the end down to 1/4" and thread with a die if needed.

-handleman, CSWP (The new, easy test)

 

[TVP]

I agree with handleman, if all this requires is a hard, smooth surface for an oil seal, then induction hardening is the optimal solution for low cost. Typically the induction hardened steel bar (SAE 1045, surface hardness in the range of 50-60 HRC) will also be hard chrome plated, ~ 10-20 micrometers thick. All you have to do is turn down the end and cut or roll the threads.

 

[fastline12]

Let me further add that there is a cross hole and two different diameters that need ground. There are a couple other features but in a nut shell, we sort of wrote off TG&P bar because of the extra processes. We "could" still drill it but will likely fight with it all the way and would still need to grind the smaller diam after the fact.


I think what we were hoping for is a process that could work as a post machining hardening process. I think we could use a 4000 series alloy and draw back to an acceptable hardness before treatment BUT we have never tried this on threads and suspect they will be damaged in heat treat? We don't usually see much dimensional change with some other 4140 parts in heat treat do see surface changes.


Nitriding maybe?

 

[TVP]

Nitriding, including salt bath nitriding (ferritic nitrocarburizing) is a possibility. You can mask threads prior to heat treatment. Depending on the production quantities needed, there are still other options available.

 

[redpicker]

Nitriding would be the process I would investigate. The case is thin with nitriding, but with only a 0.375 diameter, you will need a thin case.
You can mask-off threads and other features that do not need hardening. Most nitriding processes can be performed at 900-1100F, so you would see little distoriton or reduction in mechanical properties with a low-alloy steel provided the tempering temperature was above the nitriding temperature.

rp

 

[tbuelna]

I would use thin dense chrome plating. First of all, it is relatively quick and easy to repair a shaft surface using thin dense chrome. Secondly, thin dense chrome is much harder than nitride or carburize. Third, applying thin dense chrome plating is quick and will not create thermal distortions like nitride or carburize. And finally, there is no real benefit to having a thick hardened sealing surface layer since most elastomer seals will begin to leak once the surface scratches exceed more than around 100 micro-inches in depth.